Luminous tube apparatus



June 27, 1950 w. A. MILLIMAKE ET AL LUMINOUS TUBE APPARATUS 2 Sheets-Sheet 1 Filed April 1, 1948 #TTORNEy June 1950 w. A. MILLIMAKI ETAL 2,512,335

LUMINOUS TUBE APPARATUS Filed April 1, 1948 2 Sheets-Sheet 2 Patented June 27, 1950 UNITED STATES PATENT OFFICE LUMINOUS TUBE APPARATUS William A. Millimaki and George M. Schroeder, Waukegan, Ill., assignors, by direct and mesne assignments, to George M. Schroeder and. Albert A. Schroeder, Kenosha, Wis.

Application April 1, 1948, Serial No. 18,338

4 Claims. (Cl; 315'336) This application is a continuation-in-part of our copending application, Serial No. 637,972, filed December 29, 1945, in Luminous TubeApparatus, now abandoned.

This invention relates to luminous tube apparatus of the type wherein luminescent electric discharges are produced in gas-filled tubes.

Luminous tube apparatus of the aforesaid character may take the form of sealed glass tubes filled with neon, argon-mercury vapor, or other gases, and operating electrical connections are afforded by electrodes disposed within and adjacent the opposite ends of the tube. In the more common uses of such luminous tubes, as for vcxample, in advertising or some types of illumination, these tubes are of the cold-cathode type.

In luminous tubes of the aforesaid character it has long been recognized that the effectiveness and the useful life of the tubes has been adversely affected by the phenomenon of sputtering which produces a metallic deposit of the electrode metal on the inner tube surface adjacent to the electrodes. This sputtering of metallic particles ontothe inner surface of the glass tubing eventually forms a metallic deposit in the form of a dark or black discoloration on the inner surface of the glass tubing and causes an arcing of the current from the metallic electrode to the thus metal-coated inner surface of the. tube which, as a result thereof, becomes hot and eventually burns out. The formation of such metallic deposit also reduces the luminosity. of the tube, and results in uneven heating and consequent cracking of the glass wall of the tube. This sputtering is a familiar phenomenon ob.- served in red or rose-colored neon luminous tube signs and in white, blue, green or gold colored argon-mercury vapor signs.

An object of the present invention, therefore, is to provide a new and improved luminous tube apparatus which in use will overcome the foregoing and other objections to prior art luminous tube apparatus. Another and related object of the present invention is to reduce and substantially eliminate objectionable sputtering in-luminous tube apparatus of the aforesaid character.

In luminescent tube apparatus of the aforesaid character it is recognized that relatively large area electrodes are desirable in order to minimize the cathode drop and facilitate radiant dissipation of the heat generated as an incident to the operation of the tube, and further objects of the invention are to enable such large area electrodes to be used without objectionablesputtering,. and to prevent objectionable sputtering at 2' the open ends of elongated cup-shaped collector electrodes in such apparatus.

In affording collector electrodes in such luminous tubes so that such electrodes will have sufficient surface area to afford adequate radiant dissipation and to minimize the cathode drop, it is customary to utilize elongated cup-like or tube-like electrodes having the open ends therev of facing toward each other, or longitudinally in Wardly with respect to the ends of the tubes, and with such electrodes it is found that the objectionable sputtering phenomenon arises primarily from the ionic bombardment of the walls of the electrodes ator closely adjacent the open ends thereof. It is therefore another important object of the present invention to confine such ionic bombardment of the collector electrodes to those internal surfaces thereof that are spaced substantially from the open ends of such electrodes. Other and related objects of the present invention are to enable the electrical discharge to be confined or focused as such discharge approaches, the open end of a collector electrode; to enable such focusing effect to direct the electrical discharge into the open end of the collector electrode in spaced relation to the side walls thereof; and to enable the bombardment to be confined largely to the bottom or closed end wall of the electrode.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawing which, by way of illustration, shows preferred embodiments and. the principles thereof and what we now consider to be the best mode in which we have contemplated applying those principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

Fig, 1 is a fragmentary central vertical secjtional view of a luminous tube apparatus illustrating a typical embodiment of the invention;

Fig. 2 is a sectional plan view on line 22 in Fig. 1;

Fig. 3 is a transverse Vertical sectional view on line 33 in Fig. 2;

Fig. 4 is a fragmentary central view partly in section and partly in elevation illustrating a modified constructi-on'and form of the invention;

Fig. 5 is a central vertical sectional View of the form of the invention shown in Fig. 4;

Fig. 6 is a fragmentary view, partly in section and partly in elevation, illustrating a preferred form of feed :back conductor or Wire and connector therefor which is embodied in the form of the invention illustrated in Figs. i and 5;

Fig. 7 is an enlarged transverse sectional View on line 1-7 in Fig. 6;

Fig. 8 is a transverse vertical sectional view on line 88 in Fig. 5; and

Fig. 9 is an enlarged fragmentary sectional View of the parts shown in Fig. 8;

A typical embodiment of the present invention is illustrated in the drawing wherein itis shown as being embodied in a positive column luminous tube apparatus having an outer glass tube I10 which may be formed of any suitable, quality of glass such, for example, as lead glass, and which may be filled with any suitable ionizable gas or gas-vapor mixture such, f-orexainple, as neon gas for rose or red-colored luminous signs and the like and argon-mercuryvapor for use in white, green, blue or gold-colored luminous signs and the like.

The outer glass tube H!- is provided at its ends, only one of which isshown, with an integral sealing nipple l-i, through which a central boreor passage 12' extends, and a lead wire I 3 is: extended through and hermetically sealed inthe bore or passage l 2 of thenipple H.

In the construction of the form of the invention shown in Figs. I to 3, inclusive, We provide an electrically non-conductive inner electrodesupporting member M which may be made or any suitable electrically non-conductive ceramic or glass material such, forexample, as Pyrex glass, and this electrode-supporting member M includes a portion I5 of relatively restricted diameter-and=a portion l-fi of larger diameter. The inner glass shell or electrode-supporting memher It includes an integral nipple H- whichis provided with a central bore 18- through which a portion E9 of the metallic lead wire or rod l3 is-extended; Figs. land 2.

The form or the new luminous tubeapparatus which is illustrated in Figs. 1 to 3, inclusive, includes a substantially tubular metallic electrode 20 which may be made of anysuitable metal such, for example, as a nickel steel. alloy. The major portion or main extent of the tubular metallic electrode 20 is disposed within. and in close fitting relationship with the relatively-narrow. or restricted portion I 5 of theinner glass shell or electrode-supporting member 14 andthe inner endportion of the metallic lead-in wire or conductor member !3. is extended into and welded or soldered to the adjacent closed end portion of the-metallic-electrode, as at.2 l,, Fig. 2. The metallic electrode 20. also includes a. portion 22 which projects into the enlarged portion lit of the inner glass shell or electrode-supporting member [4 in spaced relationship with andrelative to the inner surface of the-emargedportion it of the electrode-supportingmember [4.

In the practice-of the form of. the invention shown in. Figs. 1 to 3, inclusive, we provide an electrically conductive element or substantially cylindrical shield electrode 23' in the form of a coating over substantially the entire inner surface of the enlarged portion l6 of the glass insert or electrode-supporting member l4; and the outer end wall or edgethereof. This electrode 23 is preferably of lowresistance electrically conductive initially liquid silver coating, or

other suitable low electrical resistance metal coating. For the purpose of affording a stabilized biasing potential on the electrode 23 with respect to the electrode 20, an electrical path is preferably afiorded between the lead l3 and the electrode 23. In the form illustrated such path is afforded. within the tube 20, and to accomplish this we extend or continue a relatively narrow band or strip 24 of this low resistance silver or like metallic coating over the outer surface of the enlarged. portion E6 of the inner glass supporting member M. This electrically conductive strip 20 is thus continuous at one end with the electrode 23- on the inner surface of the enlarged lJQnti' n it: of the electrode-supporting member I4, and is interrupted between its ends by a biasing; impedance which, as shown herein, takes the form of a relatively short section or block 25 of liquid platinum coating material which is arranged upon the outersurface of the relatively small portion i of the inner glass electrodesupporting member Mas a relatively thin coating which by reason of its small cross-sectional area affords a high resistance. electrical path. This biasing resistor may have a resistance of from one hundred to two hundred ohms. The electrical path thus afi'orded also. includes a further section 25 extended from the other side of the impedance or resistance element 25,. and formed of the low resistance electrically conductive liquid silver coating which is. arranged on the outer surface of: the reduced; portion ii. of the glass insert orelectrode-supporting member l4. As shown in Figs. 1 and: 2, the section 26 of low: resistance electrically conductive liquid silver coating is. extended down over the nipple ll. of the glass insert of electrode-supporting member I41 and is disposed in electrical contact with the lead wire: I3.

In the use. of the form. of the new. luminous tube apparatus. which isiillustratediinFigs. 1 to 3, inclusive, the luminous glass tube it. may be formed in any suitable shape and size and the lead wires l3 may be-connected in the conventional manner across any suitable source of electric current as, for example, l8.to 60.milliamperes at 15,000 volts in the case of neon luminous tubesigns and; in the case of argon-mercury vapor luminous tube signs, about 120 milliamperes at 7500volts.

Luminous tube apparatus of the character thus afforded is of course adapted for use in direct current circuits, or in alternating current circuits where there is a reversal of the-polarity of the operating voltage twice in each cycle of the alternating current. When the luminous tube apparatus disclosed in- Figs. 1 to 3- is thus utilized, it has been found that thezsputteringphenomenon is so'controlled and governed that-its presence or the formation of a metallic deposit on the tube cannot be noticed (many objectionable extent; and this improved operation has been found to be-due toa focusing actionthat attained by the electrode 23. Thus it has been determined' that at the-cathode, the positive column extends at least partially. into the space-within the control electrode 23; so that the Faraday dark space is actually disposed substantially at the-lipor open end of theelectrode 28; Within the control-electrode 23, however, there hasbeen found tube a positive space. charge on the. inner surface of the electrode- 23 which reduces the diameter of that portion of' the positive column, hence-the positive ions: from the negative glow area, bombard the cathode or= collector: electrode '20 in such a way as to pass into the openend of the collector electrode 20. Thus the ions as well as the electrons must strike the internal surface of the collector electrode 20 at points spaced inwardly a substantial distance from. the open end of the electrode 23, and as a result, any displacement or sputtering of electrode metal is confined to the space within the electrode so that such displaced electrode metal does not strike or become deposited on the inner surface of the tube. Another factor in this regard is the control of secondary emission, for the presence of the control electrode 23 with a charge thereon that is relatively negative with respect to the plasma and with respect to the cathode tends to repel any negative electrons that may be set in motion by the ionic bombardment of the collector electrode that is functioning as the cathode. Similarly at the electrode 23 that is serving as the anode, the charge on the related control electrode 23 is more negative than such electrode 20, and there is a positive space charge thereon so that the positive column is reduced in cross section and the electronic bombardment is directed to the inner walls of the cup. The fact that such bombardment is in both instances confined to the inner surfaces of the electrode 20 remote from the open end serves of course to reduce the possibility that the electrons resulting from such bombardment will reach the glass tube adjacent this open end of the electrode, and the control electrode 23 serves as a further protection in that the relatively negative field afforded about the open end of the electrode 20 has a suppressing action tending to prevent continued outward travel of such secondary electrons or secondary emission. Hence, the usual gathering of such secondarily emitted electrons on the inner surface of the tube l0 adjacent the open end of an electrode 20 is avoided, and a concentration of negative electrons on the tube surface is not available for combination with positive ions to form an inner metal coating on the tube as is usually experienced in conventional luminous tubes of this class.

The controlling action that is thus exerted by the electrode 23 on the ionic bombardment of the electrodes 20 has been found to be due fundamentally to its relative location and to its electrical relationship which in operation causes such electrode 23 to assume an effective biasing potential. This action is of course most important at the cathode, for it is there that the sputtering phenomenon has been most troublesome. The connection of the control electrode 23 to the electrode 20 through a biasing impedance such as the resistance 25 serves of course to impart the desired biasing potential relationship. The bias potential between the control electrode and the collector electrode should be approximately 25 volts.

In practice it has been found that the inner surface of the control electrode 23 has a dark sheath appearing thereon, and this is taken as an indication of a positive space charge which produces the focusing effect that is attained in the present structure. Moreover, by comparison of the structure with different connections or relationships between the control electrode 23 and the main electrode 20, further weight is given i -flow was found to be through the controlelectrode, but when a biasing connection was placed between these electrodes the dark sheath appeared' on the inner surface of the control electrode and-practically the entire current flow was handled by theimain electrode,- rather than through the control electrode.

A modified form of the invention is illustrated in Figs.- 4. to 9, inclusive, and those parts embodied in this form of the invention which are similar to corresponding parts in the form of the invention shown in Figs. 1 to 3, inclusive, have been given similar reference numerals followed by the distinguishing reference character a. The description of such parts will be apparent from the description of corresponding parts in the form of the invention shown in Figs. 1 to 3,

inclusive, and hence need not be repeated.

In the. form of the invention shown in Figs. 4

to 9, inclusive, we mount an electrode 23a in any suitable manner, as by a frictional lit, in the interior of the enlarged portion 16a of the inner glass shell or electrode-supporting member Ma. This electrode 23a is afforded by a substantially cylindrical shield or electrically conductive element 26 of relatively thin steel and which is provided on its outer and inner surfaces with coatings 2'! and 28, respectively, of electrically conductive andsubstantially chemically pure or socalled soft iron.

In place of the biasing connection provided by the low resistance silver coating 23 and the silver stripe or band 24-26 and interposed high resistance platinum block 25, which are embodied ing member Ma and one end portion 32 of the wire 29 is bent around one end wall of the-enlarged portion l6a of the inner glass electrodesupporting member Ma and into electrical con tact with the inner soft iron coating 28 on the steel shell or cylinder 26.

The wire 29 comprises two sections 2% and 292), the section 29a including the end portion 32 just described, and the section 29b including a substantially cylindrical connecting porti0n'33 which is bent around and into electrical contact with the connecting lead 13a, adjacent the outer end of the sealing nipple Ila on the reduced end portion l5a of the inner glass electrodesupporting member I la, Figs; 4 and 5.

The wire 29 also includes an intermediate connector or wire 290 which is disposed between the end sections 290. and 29b of the wire 29.

As best'shown in Fig. 6, each of the end sections 23a and 29b of the wire 29 has a formed or flattened clamping end portion or jaw 33 formed therein and integrally therewith. Each of these clamping jaws, 33-includes a pair of clamping arms or ears 34 and 35 which are bent around and into electrically tight contact or engagement with any end portion of the intermediate wire section 29c and, as shown in Fig. 7, each of the clamping end portions 33 is composed of an inner steel core or body 36 and an outer soft iron coating 31 thereon. Thus it will be noted that the steelflcore or body 36 of each clamping end 7 portion 33 is an integral shaped orqforme'd continuation of the steel coreorbody .30 of one of the endsections 29aor 29b of .the wire29 andthat the soft iron coating 31 on each ottheclamping jaws 33 is an integral shaped .-or formed. ccntinuation of the soitiron coating .3! on the.body 36 of the steel wire 29.

In the construction of the form of theinvention shown in Figs.'4 to 9, inclusive,.the electrode 23a that is afforded by the iron. coatedsteel shell or cylinder 2E2| -2.8 may .be frictionally or otherwise fittedinto the enlarged portionlfiw'of the inner glass electrode-supporting member. Na and the section 2901.. of the wire arranged over the outer surface of the enlarged portion Hiaand over the outer surface. of thereduced end portion I5a of the inner glass shell or electrode-supporting member Md with the end portion thereof bent around the endwall of the. enlarged portion [6a of the inner glass shell 14a and soldered or otherwise secured in electrically tight. contact to the soft iron inner coating 28 on the steel shell or cylinder 28. Similarly, the section29b of the wire 29 is laid over the outer surface of the reduced end portion l5a of the inner glass shellor electrode-supporting member Ma, with the end portion 38 of the wire section 2% bent around and soldered or otherwise electrically connected to the lead [311, as shown in Figs. 4. and 5.

The end portions of the intermediate wire. section 290 may then be inserted in the substantially cylindrical clamping portions 33 of the .wire sections 2% and 290. The cars or clamping portions 34 and 35 of the clamping members 33 may then be clamped, by means. of any suitable clamping tool, into electrically tight contact with theend portions of the intermediate wire se.ction.29c.'

In the form of the invention shown in Figs. 4 to 9, inclusive, the section ZScconstitutes the impedance or resistance for affording the desired bias on the electrode 23a, and by its resistance value, this section 290 may be so related as'tolattain the desired bias and controllingaction.

Where high current flow is desired,; the resistor 290 may be made from a material such as caricon to afford a biasing resistance of a value up to or in the order of 1000 ohms.

From the foregoing description it will'heevident that the present invention enables the .useful life of luminous tube apparatus tobe increased by control of the common phenomenon of sputtering, and more specifically it will be evident that the electrical discharge in such apparatus under the present invention is controlled in a simple and expeditious manner such that the objectionable effects of I such sputtering are avoided.

It will thus be seen from the foregoingdescription, considered with the accompanying drawing, that the present invention provides anew and improved luminous tube apparatushaving the desirable advantages and characteristics and accomplishing its intended objects, including those hereinbefore pointed out, and otherszwhich. are inherent in the invention.

We claim:

1. In a cold cathode electrode structure for use in a luminous tube apparatus, a metallic collector electrode of elongated and generally cup-shaped form having an. open forward end and a closed rear end, ametallic control. electrode physically separate from said collector electrode andsupported in surrounding and insulated relation to the open end ofsaid collector electrode and disposed so to extend a sub- 8. stantial distance beyond the open end ofsaid collector electrode, a biasingconnection extended between said electrodes and including a biasing impedance for maintaining a bias on said control electrode when said electrode structure is in use to concentrate and direct. an approaching beam to reduce its cross sectional dispersion as it passes through said control electrode and thereby cause the beam to enter the openend of the collector electrode and strike a substantial distance within the collector electrode, and insulating means closing the annular space between said control electrode and said collector electrode to block rearward discharge of slow secondaries between said electrodes.

2. In a cold cathode electrode structure for use in a luminous tube apparatus, a collector electrode made from a refractory metal to afford an elongated and generally cup-shaped form to afford an open forward end and a closed rear end, a control electrode made from a refractory metal and physically separate from said collector electrode, insulating means supporting said control electrode in surrounding and insulated relation to the open end of said collector electrode with said control electrode disposed so as to extend a substantial distance beyond the open end of said collector electrode, said insulating means being so formed and positioned as to close the space between said electrodes at the rear end of said control electrode so as to prevent rearward discharge of slow secondar electrons rearwardly between said electrodes, and a biasing connection extended between said electrodes and including a biasing impedance for maintaining a bias on said control electrode when said electrode structure is in use to concentrate and direct an approaching beam toreduce its cross sectional dispersion as it passes through said control electrode and thereby cause the beam to enter the open'end of the collector electrode andstrike a substantial distance within the collector electrode.

3. In a cold cathode luminous tube apparatus, an elongated glass tube having an ionizable gas sealed therein, electrode structures disposed within said tube at opposite-ends thereof, and at least one of said electrode structures comprising a metallic collector electrode of elongated and generally cup-shaped form having an open forward end and a closed rear end, a metallic control electrode physically separate from said collector electrode and supported in surrounding and insulated relation to the open end of said collector electrode and disposed so as to extend a substantial distance beyond the open end of saidcollector electrode, a biasing connection extended between said electrodes and including a biasing. impedance for maintaining a bias on said control electrode to concentrate and direct an approaching beam to reduce its cross sectional dispersion asit passes through said control electrode and thereby cause the beam to enter the open end of the collector electrode and strike a substantial distance withinthe collector electrode,yand insulating means closing the annular space between said control electrode and said collector electrode to block rearward discharge of slowsecondaries between said electrodes.

4. Ina cold cathode luminousltube apparatus, an elongated glass tubehavingv an ionizable gas sealed therein, electrode structures disposed within" said tube at opposite ends thereof, and at least one of said electrode. structures comprising a collector electrode formed frorn'arefractory metal and of elongated and generally cup-shaped form having a closed rear end and an open forward end, a control electrode formed from a refractory metal and separate from said collector electrode, means supporting said control electrode in surrounding and insulated relation to the open end of said collector electrode and with said control electrode disposed so as to extend a substantial distance beyond the open end of said collector electrode, a biasing connection extended between said electrodes and including a biasing impedance for maintaining a bias on said control electrode when said electrode structure is in use to concentrate and direct an approaching beam to reduce its cross sectional dispersion as it passes through said control electrode and thereby cause the beam to enter the open end of the collector electrode and strike a substantial distance within the collector electrode, and insulating means closing the annular space between said control electrode and said collector electrode to block rearward discharge of slow secondaries between said electrodes.

WILLIAM A. IVHLLIMAKI. GEORGE M. SCHROEDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,808,826 Teasdale June 9, 1931 1,856,758 Goodard May 3, 1932 1,877,716 Claude Sept. 13, 1932 1,942,627 Wiley Jan. 9, 1934 2,008,066 Ende, July 16, 1935 2,020,393 Woolrich Nov. 12, 1935 2,314,134 Eknayan Mar. 16, 1943 2,441,260 Cortese May 11, 1948 2,473,413 Cortese June 14, 1949 FOREIGN PATENTS Number Country Date 523,923 Great Britain July 25, 1940 

